I’m thinking the ECU was de-rating the motor due to the water temps. I’ve done the Payson drive more than once with my Ram 1500 ED and it would accelerate well past 80mph when I needed to pass people. Something isn’t right w yours, but a dealership tech isn’t ever gonna figure it out. Those guys are just parts swappers, not mechanics.Bone stock no towing. It was 80mph at about 3k rpm wouldn't go any faster.
Unless you stick a thermocouple directly into the coolant stream, that reading isn't going to tell you much. That plastic hose connector is going to insulate much of the heat especially since it is made using a glass or carbon filled polymer. The reflectivity of the object can also greatly affect your readings.Lookie here...Maybe the sensor is on the crown of the piston...lol. Such bullshit